Condensate demineralization

ABSTRACT

In a demineralization apparatus, a mixed bed of a gel type cation exchange resin having a moisture holding capacity of 41% or less or a degree of crosslinkage of 12% or greater is employed along with a porous type anion exchange resin. As a result, oxidation degradation of the cation exchange resin due to hydrogen peroxide can be inhibited and the performance of the ion exchange resins and of the condensate water demineralizer can be stabilized and maintained for a long period of time.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a condensate demineralization,and especially to an apparatus and a method for use in purification(demineralization) of condensate in power plants.

[0003] 2. Description of the Related Art

[0004] In a facility such as, for example, a pressurized water reactornuclear power plant, because there is a need to constantly maintain thequality of water within a steam generator pure, condensate water flowinginto the steam generator from a condenser is purified by a condensatedemineralizer(s). A boiling water reactor nuclear power plant is alsoequipped with a condensate demineralizer(s) for purifying condensatebecause there is a need for constantly maintaining the quality of waterpure.

[0005] The condensate demineralizer is provided in order to demineralizecondensate water by removing, using ion exchange resins, metalimpurities leached from materials of construction such as pipes and saltimpurities resulting from leakage of sea water used as the cooling waterof the condenser.

[0006] The condensate demineralizer usually consists of a plurality ofdemineralization columns filled with a mixture of anion exchange resinand cation exchange resin for processing the condensate water and anexternal regeneration system which is designed to regenerate(rejuvenate) the ion exchange resins which have been exhausted, that is,when a breakthrough point has been reached. The exhausted ion exchangeresins are transferred from the demineralization column to theregeneration system outside the demineralization section. The ionexchange resins thus regenerated are returned to the demineralizationsection for reuse.

[0007] The ion exchange resins can generally be categorized into eithergel type or porous type, such as macroporous (MP) and macroreticular(MR), according to the structural characteristics. In those applicationsin which ion exchange resins are regenerated more frequently, poroustype ion exchange resins with a greater physical strength (resistant toosmotic shocks) are generally used in order to allow for the swellingand contraction of the ion exchange resins.

[0008] When, on the other hand, the regeneration is not frequentlyrequired, such as in a case for a condensate water demineralizer for aboiling water reactor nuclear power plant, gel type ion exchange resinswith a greater ion exchange capacity are typically used.

[0009] In either case, the anion exchange resin to be mixed and usedwith the cation exchange resin is usually of the same type as the cationexchange resin in terms of the porosity.

[0010] In any way, the performance of the ion exchange resin decreasesas it is used over the years, and thus, there is a need for replacingthe ion exchange resins once every few years. Performance decrease overyears of use may be due to slough of organic materials such aspolystyrene sulphonate (hereinafter abbreviated to “PSS”) from thecation exchange resin under an oxidizing atmosphere. In particular,hydrazine is commonly added to condensate water of a pressurized waterreactor nuclear power plant to prevent rust in the pipes. The hydrazineoxidizes and decomposes upon contact with air used for scrubbing or thelike performed during the regeneration of the ion exchange resin,leading to generation of hydrogen peroxide. As a result, the cationexchange resin decomposes and PSS or the like is given off.

[0011] In a boiling water reactor nuclear power plant, no chemical isadded to condensate water for preventing rust, and demineralized wateras such is used. Thus, normally, ion exchange resins are not oxidized byan oxidizing agent in the condensate water demineralizer. However,during periodic checkups of the power plant, water within the nuclearreactor is radiation decomposed, thereby generating hydrogen peroxide.The water within the nuclear reactor is then passed through thecondensate water demineralizer after the operation is restarted. Becauseof this, water containing hydrogen peroxide is supplied to thecondensate water demineralizer at a boiling water reactor nuclear powerplant, promoting decomposition of the cation exchange resin just as inthe case with a pressurized water nuclear power plant.

[0012] Moreover, leachables generated by the decomposition of the cationexchange resin, including the PSS described above, attach themselves tothe anion exchange resin and contribute to a reduction of reactivity ofthe anion exchange resin. When the reactivity of the anion exchangeresin is reduced, its performance of the removal of anion impurities(such as Cl⁻ or SO⁻² ₄) contained in condensate water is reduced, waterquality in the nuclear reactor (boiling water reactor nuclear powerplant) or in the steam generator (pressurized water nuclear power plant)is reduced, and corrosion of construction materials is promoted.

[0013] Furthermore, as a result of the reduction in the reactivity ofthe anion exchange resin, leachables from the cation exchange resin flowinto the condensate water without being captured by the anion exchangeresin, thereby resulting in a deterioration of the treated waterquality.

SUMMARY OF THE INVENTION

[0014] One object of the present invention is to provide condensatewater demineralization which can be used for processing condensatewater, without giving rise to any serious degradation of ion exchangecapacities. This demineralization method is particularly suitable fortreating condensate water commonly found in power plants includingpressurized water and boiling water reactor nuclear power plants.

[0015] The present inventors, after years of research to achieve theabove object, found that by using a combination of a specific gel typecation exchange resin and a specific porous type anion exchange resin, astable performance can be maintained even when the ion exchange resinscome in contact with water containing hydrogen peroxide.

[0016] Specifically, the present invention relates to condensate waterdemineralization wherein a mixed bed of a gel type cation exchange resinand a porous type anion exchange resin is used, the cation exchangeresin having a moisture holding capacity of 41% or less or acrosslinkage of 12% or greater.

BRIEF DESCRIPTION OF THE DRAWING

[0017]FIG. 1 is a flowchart for a pressurized water reactor nuclearpower plant equipped with a condensate water demineralizer of thepresent invention.

[0018]FIG. 2 is a flowchart for a boiling water reactor nuclear powerplant equipped with a condensate water demineralizer of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] The inventors found that a specific combination of a gel typecation exchange resin and a porous type anion exchange resin can be usedto stabilize for a long period of time the performance of the ionexchange resins in a condensate water demineralizer.

[0020] Specifically, porous type cation exchange resins such asAMBERLITE 200C from Rohm and Haas Co. and DIAION PK228 from MitsubishiChemicals Inc., which are typically used in a pressurized water reactornuclear power plant, have levels of crosslinkage of 20% and 14%,respectively. The inventors observed that even though these cationexchange resins exhibit good resistance to oxidation due to their highlevels of crosslinkage, leachables from these cation exchange resinsstill affect the anion exchange resins and significantly deteriorate theperformance of the anion exchange resins.

[0021] This is likely caused, not by macromolecular leachables which arereleased by the oxidation of the resin, but by resin fines produced byattrition (physical loading) to which porous type ion exchange resinsare liable.

[0022] To the condensate water in a pressurized water reactor nuclearpower plant is added ammonia as a rust preventing reagent and hydrazineas a deoxidizing reagent. While in a once-through boiler of a thermalpower plant, because hydrazine is completely decomposed at the boiler,hydrazine is not transported to the vapor side, and thus, hydrazine willnot be entrained to the condensate water, in a pressurized water reactornuclear power plant, on the other hand, part of hydrazine is carried tothe condensate water demineralizer.

[0023] A regeneration operation is performed periodically in thecondensate water demineralizer, and during this periodic operation airscrubbing is performed to remove a small amount of metal oxides in thecondensed water which have deposited on the ion exchange resins. In thescrubbing operation, air is blown in, the resins are agitated bybubbles, the metal oxides are dislodged from the resins, and theisolated metal oxides are removed by water backwash.

[0024] During the air scrubbing, hydrazine, small amounts of metals, andair are mixed, and hydrazine decomposes through auto oxidation using themetals as catalysts to thereby generate hydrogen peroxide. The cationexchange resin is then oxidized by the hydrogen peroxide, and PSS or thelike will eventually leach out.

[0025] In a boiling water reactor nuclear power plant, no reagent suchas a rust-preventing reagent is added to the condensate water anddemineralized water as such is used, and thus, normally, the ionexchange resins at the condensate water demineralizer are not oxidized.However, during periodic maintenance, the water within the nuclearreactor is radiation decomposed and hydrogen peroxide is generated. Thewater within the nuclear reactor is then passed through the condensatewater demineralizer when the operation is restarted. Because of this,the water supplied to the condensate water demineralizer in a boilingwater reactor nuclear power plant contains hydrogen peroxide, whichbring about oxidation decomposition of the cation exchange resin, with aresult similar to the case with a pressurized water reactor nuclearpower plant.

[0026] In the present invention, a gel type cation exchange resin isused. In particular, considering the characteristics of the resins, itis preferable to use a gel type cation exchange resin which has amoisture holding capacity of 41% or less or a crosslinkage of 12% orgreater. More preferably, the moisture holding capacity is between 30%and 38% or the crosslinkage is between 14% and 16%.

[0027] The moisture holding capacity to be used in the above describedcriteria is a value determined when the ion form is a standard form(sodium form) as will be described later. When the moisture holdingcapacity is represented for a case in a regenerated form (hydrogenform), it is preferable to have a moisture holding capacity of 49% orless, and more preferably in a range between 37% and 46%.

[0028] The gel type cation exchange resin used in the present inventioncan be any of the known gel type cation exchange resins. The resin can,for example, be manufactured by copolymerizing an aromatic monovinylmonomer such as styrene, vinyltoluene, vinylxylene, ethylstyrene, andchlorstyrene, with an aromatic polyvinyl monomer such as divinylbenzeneand divinyltoluene, and then introducing cation exchange radicals. It ispossible to use both aromatic polyvinyl monomer and ester polyvinylmonomer as a polyvinyl monomer, and it is preferable to use a gel typecation exchange resin derived from such polyvinyl monomers. As an esterpolyvinyl monomer, for example, ethylene glycol dimethacrylate,diethylene glycol dimethacrylate, neopentyl glycol dimethacrylate,trimethylol propane trimethacrylate, or the like, or an equivalentacrylate can be used independently or as a mixture.

[0029] Moisture holding capacity as used in the present specificationrefers to the ratio of water content measured when the water within theresin capillary is adjusted to a state of saturation equilibrium. In thespecification, the moisture holding capacity refers to a value for a geltype strong acid cation exchange resin with a standard ion form (sodiumform). In the examples described later in this specification, this valuewas measured by the following procedure.

[0030] (a) A sample resin having a standard form (sodium form) andmoisture content at an equilibrium was prepared.

[0031] (b) Approximately 5 g of the sample resin prepared as in (a)above was placed into each of two flat balance bins adjusted to aconstant weight to weigh the sample weight to an accuracy of 1 mg.

[0032] (c) Each sample was placed in a drying container pre-adjusted to110±5° C., and allowed to dry for 24 hours.

[0033] (d) Each sample was allowed to cool for approximately 30 minutesin a desiccator.

[0034] (e) The measurement bin was sealed and the mass of each bin wasmeasured, and then the differences (a g) between the bins before dryingand the bins after drying, that is, between the weight of the resin inwhich the moisture content is at an equilibrium and the weight of theresin after the drying, was found and used to calculate the moistureholding capacity (%) using the following formula.

M ₁ =a/W×100

[0035] where M₁ is the moisture holding capacity (%) and W is the weight(g) of the resin in which the water content is at an equilibrium.

[0036] The measurement of the weights of the resin with the moisturecontent at an equilibrium and after the drying was simultaneously madefor two samples of the identical resin, and, if the two results differedby more than 0.5%, the examination was repeated until two resultscoinciding with each other within a difference of 0.5% were obtained.When the two results match within 0.5% difference, the average value ofthese results was adopted as the examination result.

[0037] The level of crosslinkage in the present invention refers to thedegree of crosslinkage by the polyvinyl monomer, and specifically,refers to the weight ratio (%) of divinylbenzene with respect to all thevinyl monomers. When an aromatic polyvinyl monomer and ester polyvinylmonomer are both used for the resin, however, the level of crosslinkagecannot be determined by the above definition of the level ofcrosslinkage. In such cases, a preferable gel type cation exchange resincan be selected and determined based on the moisture holding capacity.

[0038] In a gel type ion exchange resin, the moisture holding capacityand the degree of crosslinkage have a close relationship to each other,and, generally, as the degree of crosslinkage increases, the moistureholding capacity decreases in a gel type ion exchange resin.

[0039] When the moisture holding capacity exceeds 41% or the degree ofcrosslinkage is below 12% in a gel type cation exchange resin, theresistance to oxidation is low, and such a gel type cation exchangeresin is therefore not preferred.

[0040] As a gel type cation exchange resin for use in the presentinvention, any commercially available cation exchange resin which has amoisture holding of 41% or less or a degree of crosslinkage of 12% orgreater can be used. Examples of suitable commercially available geltype cation exchange resins includes AMBERLITE IR-124, AMBERLITE XT-1006(trade name, Rohm and Haas Co.), DIAION SK112, and DIAION SK116 (tradename, Mitsubishi Chemicals Inc.).

[0041] In the present invention, porous type anion exchange resins to beused with the gel type cation exchange resin includes both MR(macroreticular) type and MP (macroporous) types.

[0042] In the present invention, a porous type anion exchange resin isused because, in general, a porous type anion exchange resin has abetter resistance to fouling than a gel type anion exchange resin.

[0043] Any known and/or commercially available porous type anionexchange resin with a diameter between 100 and 1000 μm can be used inthe present invention, and can be either strong by basic or weaklybasic.

[0044] Examples of suitable commercially available porous type anionexchange resins include AMBERLITE IRA-900, AMBERLITE IRA-910 (tradename, Rohm and Haas Co.), DIAION PA308, DIAION PA312, DIAION PA316,DIAION PA408, DIAION PA412, DIAION PA418 (trade name, MitsubishiChemicals, Inc.), DOWEX MSA-1, DOWEX MSA-2 (trade name, Dow Co.), andLEWATIT MP500 (trade name, Bayer Co.). It is preferable that a poroustype anion exchange resin employed in the present invention has aspecific surface area of 1 m²/g or more. If the specific surface area isless than 1 m²/g, the capability for adsorbing leachables from the geltype cation exchange resin is low while the reduction in reactivitystill high even when the quantity of leachables is small, and thereforenot preferred.

[0045] The ratio of the gel type cation exchange resin and the poroustype anion exchange resin to be used in the present invention, (gel typecation exchange resin):(porous type anion exchange resin), is preferablywithin a range of 1:2 to 3:1 (volume ratio in standard form). The geltype cation exchange resin is usually used in an H type, and the poroustype anion exchange resin is usually used in OH type.

[0046] The condensate water demineralizer of the present invention iseffective in applications where the ion exchange resins come in contactwith oxidizing materials, especially hydrogen peroxide. In other words,the demineralizer can be preferably used as a condensate waterdemineralizer in pressurized water reactor nuclear power plants and inboiling water demineralizer nuclear power plants. The condensate waterdemineralizer is effective for cases where the cation exchange resincomes in contact with hydrogen peroxide.

[0047] The condensate water demineralizer of the present invention ischaracterized by the combination of the ion exchange resins to be used,but the overall structure is equivalent to that of the conventionalcondensate water demineralizers, and thus, its structure will not bedescribed in detail.

[0048] “Demineralizer Structure”

[0049] Operational flow of the condensate water demineralizer used inpressurized water reactor nuclear power plants will now be described byreferring to FIG. 1.

[0050] In a pressurized water reactor nuclear power plant, steam issupplied to a turbine 11 which is driven by the steam to generate power.The steam discharged from the turbine 11 is introduced to a condenser 1,where the steam is cooled and becomes condensate water. Sea water or thelike is used for cooling the condenser 1.

[0051] The condensate water obtained at the condenser is supplied to acondensate water filtering apparatus 3 by a condensate water pump 2,where solid materials are filtered out. There are some cases where nocondensate water filtering apparatus is provided. The filtrate flowingout of the condensate water filtering apparatus 3 is fed to a condensatewater demineralizer 4 of the present invention where the condensatewater is purified (demineralized). In other words, the condensate waterdemineralizer 4 is filled with a gel type cation exchange resin and aporous type anion exchange resin, and various ions included in thecondensate water are removed.

[0052] The condensate water which is purified (demineralized) at thecondensate water demineralizer 4 is then heated at a low pressure feedwater heater 5 and degassed at a degasifier 6. The degassed condensatewater is pressurized to a predetermined pressure by a feed pump 7,heated at a high pressure feed water heater 8, and fed to a steamgenerator 9. At the steam generator 9, heat is exchanged with a hightemperature and high pressure water supplied from a nuclear reactor 10,so that the condensate water becomes a steam, which is then supplied tothe turbine 11, where a power generator 12 is driven to generate power.

[0053] In the power generation cycle, ammonia and hydrazine are addeddownstream (at a point near the steam generator 9) of the condensatewater demineralizer 4 for preventing rust. These compounds are thencirculated via the steam generator 9 forward to the condensate waterdemineralizer 4. In particular, the steam generator 9 is typicallyoperated at approximately 270° C. which is lower than the temperature ina boiler at a fossil-fueled power plant. Because of this, only a portionof hydrazine is decomposed, and there will be some hydrazine remainingin the condensate water, which is sent to the condensate waterdemineralizer 4.

[0054] The condensate water demineralization 4 is regenerated when itsion exchange capacity is exhausted. Regeneration is effected by passinga hydrochloric acid solution for the cation resin and a sodium hydroxidesolution for the anion resin. During the regeneration, air scrubbing iscarried out to dislodge small amounts of metal oxides from the resinsurfaces. The dislodged metal oxides are then removed from the system bywater backwash.

[0055] During the air scrubbing, hydrazine oxidizes itself(autooxidation) with the small amounts of metal as a catalyst, andhydrogen peroxide is generated. While in a conventional system a cationexchange resin is generally vulnerable to hydrogen peroxide and normallyliable to degradation, in the present invention, a gel type cationexchange resin with a predetermined degree of crosslinkage is used, andtherefore, the cation exchange resin is resistant to decomposition byhydrogen peroxide, thereby increasing the lifetime of the cationexchange resin. Moreover, because the cation exchange resin does notdecompose as easily, the lifetime of the anion exchange resin can alsobe elongated. In particular, because a porous type resin is used as theanion exchange resin, the anion exchange resin has a larger surfacearea, resulting in reduction of lifetime degradation due to PSS or thelike adhering to the resin.

[0056] Because blowdown water in the steam generator 9 is generally alsosent to the condenser 1, hydrazine also flows into the condensate waterdemineralizer 4 from this route.

[0057]FIG. 2 shows the flow of a condensate water demineralizer used ina boiling water reactor nuclear power plant.

[0058] In a boiling water reactor nuclear power plant, the plantstructure is basically identical to the pressurized water reactornuclear power plant, with the exception that the condensate water isdirectly supplied to a nuclear reactor 20 where the condensate water isheated and vaporized. In other words, the steam generated at the nuclearreactor 20 is supplied to a turbine 11 where a power generator 12 isdriven to generate power. The steam from the turbine 11 is thencirculated to the nuclear reactor 20 via a condenser 1, a condensatewater pump 2, a condensate water filter 3, a condensate waterdemineralizer 4, a low pressure feed water heater 5, feed water pump 7,and high pressure feed water heater 8.

[0059] In such a boiling water reactor nuclear power plant, water withinthe nuclear reactor 20 is decomposed by radiation when the powergeneration is interrupted, resulting in generation of hydrogen peroxide.The steam generated in the nuclear reactor 20 is eventually transferredto the condenser 1, and thus, water containing hydrogen peroxide flowsin to the condensate water demineralizer 4. Therefore, just as in thecase of the pressurized water reactor nuclear power plant exampledescribed above, degradation of the cation exchange resin tends to occurat the condensate water demineralizer 4. In the present embodiment, theeffects and damages due to hydrogen peroxide are inhibited by using agel type cation exchange resin with a given degree of crosslinkage.

[0060] The results of various experiments will now be explained.

[0061] The experiments were performed using each of the ion exchangeresins shown in Tables 1 (showing cation exchange resins) and 2 (showinganion exchange resins). TABLE 1 MOISTURE DEGREE OF HOLDING RESIN BRANDMANUFACTURER TYPE CROSSLINKAGE (%) CAPACITY (%)* Ambelite Rohm and HaasPorous 20 49 200CP Diaion Mitsubishi Porous 14 40 PK228 ChemicalsAmberlite Rohm and Haas Gel  8 46 IR120B Amberlite Rohm and Haas Gel 1241 IR124 Amberlite Rohm and Haas Gel 16 37 XT1006

[0062] TABLE 2 SPECIFIC RESIN BRAND MANUFACTURER TYPE SURFACE AREAAmberlite Rohm and Haas Gel 0.1 or less IRA400 Amberlite Rohm and HaasPorous Approximately 18 IRA900

EXAMPLE 1

[0063] 100 ml each of the five types of cation exchange resins and 100ml of anion exchange resin Amberlite IRA 400 were measured. Each of thecation exchange resins was mixed with the anion exchange resin andfilled in an acrylic column with an inside diameter of 25 mm. Scrubbingair was introduced from the bottom of the column to create anenvironment where the resins are rubbed.

[0064] Because iron rust (commonly called cruds) is present in thecondensate water, 1 g/L-resin of iron oxide was added to simulate this,and scrubbing was performed for 16 hours.

[0065] Then, in order to check any effect of the cation exchange resinon the fouling of the anion exchange resin, the mass transfercoefficient (hereinafter abbreviated to “MTC”) of the anion exchangeresin was measured. The results are shown in Table 3. TABLE 3 MTC VALUEFOR ANION EXCHANGE RESIN BRAND OF COMPANION CATION AMBERLITE IRA400EXCHANGE RESIN (×10⁻⁴ m/sec.) Amberlite 200CP 1.1 Diaion PK228 1.2Amberlite IR120B 2.0 Amberlite IR124 2.0 Amberlite XT1006 2.0

[0066] The measurement of MTC of the anion exchange resin was made asfollows. New cation exchange resins regenerated under the conditionsshown in Table 4 were prepared, each of these resins was mixed with ananion exchange resin which is treated as described above, separated andregenerated, in a mixing ratio of {fraction (2/1)}, and the mixture wascharged into a column. Feed water with an NH₃ concentration of 1500 ppband an Na₂SO₄ concentration of 300 ppb was passed through the columnwith a linear velocity (LV) of 120 m/hour, and the SO₄ concentration ofthe outlet (treated) water from the column was measured. Then, the SO₄concentration of the treated water at the time when this SO₄concentration had stabilized and the SO₄ concentration of the feed waterat the column inlet were measured. Finally, the MTC value was calculatedby the following formula using these measured SO₄ concentration values,and void ratios of the anion exchange resin and the particle size of theresin which were separately measured.

K={⅙(1−ε) R}·{F/(A×L)}·d·ln(C ₀ /C)

[0067] where K is the mass transfer coefficient (m/sec.), ε is the voidratio, R is the ratio of anion exchange resin, F is the flow rate offeed water (m³/sec.), A is the cross sectional area of the column (m²),L is the height of the resin layer (m), d is the particle size of theresin (m), C₀ is the SO₄ concentration at the column inlet, and C is theSO₄ concentration at the column outlet. TABLE 4 Regeneration ConditionsRESIN CATION EXCHANGE RESIN ANION EXCHANGE RESIN REGENERATION LEVEL 35%HCL, 350 g/L-R 100% NaOH, 200 g/L-R REGENERANT 5% 7% CONCENTRATIONREGENERANT VELOCITY SV* = 4 SV = 4 (55° C.) (Room Temperature)DISPLACEMENT SV/TIME SV = 4, 60 minutes SV = 4 (55° C.) (RoomTemperature) RINSE SV/TIME SV = 10, 60 minutes SV = 10, 60 minutes (RoomTemperature) (Room Temperature)

[0068] As is apparent from the results shown in Table 3, porous cationexchange resins 200CP and PK228 led to significant drops in the MTC ofthe anion resin, which serves as an indicator of the reactivity of theanion exchange resin, from the value 2.0×10⁻⁴ m/sec. for a new resin.The gel type cation exchange resins, on the other hand, resulted in nosignificant drop in the MTC value of the anion resin, and thus,considered to be good for use in the condensate water demineralizer inaccordance with the present invention.

EXAMPLE 2

[0069] 100 ml each of the five types of cation exchange resins asdescribed above and 200 ml of anion exchange resin Amberlite IRA400 weremeasured. Each of the five cation exchange resins mixed with the anionexchange resin was charged into an acrylic column with an insidediameter of 25 mm. Feed water containing hydrogen peroxide with aconcentration of 3 ppm was passed through the column with a flow rate of40 m/h. Iron ions were added beforehand so that the cation exchangeresin was loaded with 20 g Fe/L-resin.

[0070] The feed water was passed for 16 hours under the above-mentionedconditions. Then, the MTC value of the anion exchange resin was measuredin order to check any fouling effect of the cation exchange resins onthe anion exchange resin. The results are shown in Table 5. TABLE 5BRAND OF COMBINED MTC VALUE OF ANION CATION EXCHANGE RESIN EXCHANGEDEGREE OF AMBERLITE IRA400 RESIN CROSSLINKAGE (%) (×10⁻⁴ m/sec.)Amberlite 200CP 20 2.0 Diaion PK228 14 2.0 Amberlite IR120B  8 <0.5Amberlite IR124 12 1.8 Amberlite XT1006 16 2.0

[0071] As can be seen from Table 5, the effects of oxidizing agentsdepend on the degree of crosslinkage of the cation exchange resins. Theresults indicate that the effect starts to decrease around at a level ofcrosslinkage of 12% and then stabilizes.

EXAMPLE 3

[0072] Example 3 was performed with identical conditions as in example 1except that Amberlite IR124 was used as a cation exchange resin, twotypes of anion exchange resins, porous type Amberlite IRA900 and geltype Amberlite IRA400 were used for combining with the cation exchangeresin, and the resistance to fouling of the anion exchange resin wasevaluated using the MTC value as a indicator. The results are shown inTable 6. TABLE 6 MTC VALUE OF ANION CATION EXCHANGE COMPANION ANION TYPEOF ANION EXCHANGE RESIN RESIN BRAND EXCHANGE RESIN EXCHANGE RESIN (×10⁻⁴m/s) Amberlite IR124 Amberlite Porous 2.0 IRA900 Amberlite IR124Amberlite Gel <0.5 IRA400

[0073] As is apparent from Table 6, a porous type anion exchange resinis better in the resistance to fouling the pollution resistivity than agel type anion exchange resin when combined with the cation exchangeresin.

[0074] As described, according to the present invention, the condensatewater demineralizer performance and the ion exchange resin performancecan be maintained for a longer period of time, and thus, thedemineralizer is particularly suitable for processing condensate waterwithin a pressurized water reactor or boiling water reactor nuclearpower plant.

What is claimed is:
 1. A condensate water demineralizer for treatingcondensate water in a power plant, said condensate water demineralizercomprising a mixed bed of a gel type cation exchange resin and a poroustype anion exchange resin, said cation exchange resin having a moistureholding capacity of at most 41% or a degree of crosslinkage of at least12%, wherein said power plant is a nuclear power plant.
 2. A condensatewater demineralizer of claim 1, wherein said nuclear power plant is apressurized water reactor nuclear power plant.
 3. A condensate waterdemineralizer of claim 1, wherein said nuclear power plant is a boilingwater reactor nuclear power plant.
 4. A condensate water demineralizerof any one of claims 1 through 3, wherein the specific surface area ofsaid porous type anion exchange resin is at least 1 m²/g.
 5. Acondensate water demineralization method for treating condensate waterat a nuclear power plant, wherein a mixed bed of a gel type cationexchange resin and a porous type anion exchange resin is used fordemineralizing condensed water, said cation exchange resin having amoisture holding capacity of at most 41% or a degree of linkage of atleast 12%.
 6. A condensate water demineralization method of claim 5,wherein said nuclear power plant is a pressurized water reactor nuclearpower plant.
 7. A condensate water demineralization method of claim 5,wherein said nuclear power plant is a boiling water reactor nuclearpower plant.
 8. A condensate water demineralization method of any one ofclaims 5 through 7, wherein the specific surface area of said poroustype anion exchange resin is at least 1 m²/g.